1. Field of the Invention
This invention relates generally to a bucket tip construction for open circuit liquid cooled turbines and more specifically to an improved means for removing vaporized and liquid coolant from the turbine bucket tip.
2. Description of the Prior Art
Ultra-high temperature (UHT) gas turbines operate in a range from 2500.degree. F. to 3500.degree. F., providing as much as 200% more power and achieving as much as 50% greater thermal efficiency than conventional gas turbines. Materials and construction methods employed in the manufacture of such turbines dictate that the buckets thereof be provided with open circuit liquid cooling. Examples of open circuit liquid cooled turbine buckets are disclosed in U.S. Pat. Nos. 3,446,481 and 3,446,482 to Kydd and assigned to the assignee of the present invention.
Due to environmental considerations and the minimization of the requirement for make-up coolant, it has been the practice to recover as much liquid coolant which exits the bucket tip as possible. However, due to the high energy flow of motive fluid in an ultra-high temperature gas turbine, substantial amounts of liquid coolant may be discharged from the bucket and become entrained in the motive fluid flow. Should the liquid coolant become so entrained, impingement of the liquid coolant upon successive stages of turbine buckets can cause the erosion of the bucket airfoil surfaces thereby requiring accelerated maintenance and/or replacement of the buckets. Moreover, it has been found that the subsequent recirculation of liquid coolant through the buckets or the channeling of liquid coolant to the feed water input to a steam turbine is achieved more economically if liquid coolant with only minimal amounts of vaporized coolant entrained therein is recovered from the bucket than if the recovered liquid coolant has substantial quantities of vaporized coolant entrained therein.
As the liquid coolant flows through the gas turbine bucket, substantial quantities of the coolant are vaporized and, like the unvaporized coolant, are removed. It has been found that this removal of coolant from such a UHT bucket has associated therewith a certain amount of energy recoverable from the discharge of the vaporized coolant from the bucket. That is, if the coolant discharge is in a rearward direction relative to the direction of rotation of the bucket, the reaction force on the bucket from the coolant discharge stream adds energy to the rotating bucket thereby increasing its power output capability. Such schemes for the energy recovery of vaporized coolant discharged from the bucket are known as power augmenters, a suitable construction being disclosed and claimed in U.S. Pat. No. 3,816,022 to Day, incorporated herein by reference, and assigned to the assignee of the present invention. Therefore, it is desirable to retain the capabilities of power augmentation associated with UHT buckets while recovering the liquid coolant from the bucket tip.
Accordingly, it is an object of the present invention to provide a bucket tip construction for open circuit liquid cooled turbines wherein liquid and vaporized coolant are separately discharged from a particular bucket thereby increasing the efficiency of the recovery of liquid coolant.
It is another object of the present invention to provide a bucket tip construction for open circuit liquid cooled turbines whereby bucket erosion due to the entrainment of liquid coolant in the motive fluid after discharge from the bucket, is minimized.
It is another object of the present invention to provide a bucket tip construction for open circuit liquid cooled turbines wherein power augmentation is achieved from the discharge, from the bucket, of vaporized coolant relatively free of liquid coolant.